This is in response to a question about cooking potato vareniki from World Market in SF.
I don't have a precise method. I put the frozen vareniki into moderately boiling water (not a hard boil, or the dumplings will burst). I cook them al dente, then drain them. I then brown them in clarified (or plain) butter over medium heat.
Maybe check the dumplings for cracks before cooking them. I've often found cracks in them, and in that case they are guaranteed to break.